Sheet metal joint and box and method of making same



D- 8, 1959 w. PFlsTER ETAL 2,916,181

SHEET METAL JOINT AND BOX, AND METHOD OF MAKING SAME Filed oct. e. 1954SHEET METAL JOINT AND BOX AND METHOD OF MAKING SAME I William Pfister,Livingston, NJ., and Alexander R. Norden, New York, N.Y., assignors toFederal Pacili'c Electric Company, a corporation of Delaware The presentinvention relates to sheet metal joints and yto boxes using such joints,and it also relates to methods vof making sheet metal joints and boxes.

' Over the years sheet metal parts have been joined .to- .gether in manyways, as with rivets, spot-welds, and with integral projectionsextending from one metal sheet through a hole in another sheet and bentover to hold the sheets together. The present invention has as an objectvthe provision of a new form of sheet metal joint having certainadvantages over such joints known previously, and a related object is toprovide a novel method of making sheet metal joints. A funther object ofthe invention resides in providing a simplified and improved box jointand a novel method of making boxes whose walls are joined in the novelmanner.

A'feature of this invention is the great strength of the :novel jointsproduced. An additional feature is the generous tolerances permissiblein the joint forming operations. A further feature lies in a reductionin the number of operations involved in making boxes with joined walls.`Other aspects of the invention and features of novelty will be apparentfrom the detailed description of an embodiment of the invention givenbelow.

'Ihis illustrative embodiment will be seen to involve a four-walled boxhaving one pair of walls formed with edge portions turned in along theinside surfaces of the other pair of walls. These in-turned edgeportions may be referred to as inner metal sheet members or, moresimply, as inner sheets or inner walls. Tongues are struck out of theinner sheets, these tongues projecting outward ,through holes in Itheovenlying pair of walls. The inner- `sheet tongues leave spaces in themetal from which they l vare struck. The portions of the tongues thatproject .from the inner sheet beyond the outer metal sheet are bentacross the outer surface of that outer sheet, and are pressed hardenough to drive metal from the outer sheet lUnited States Patent()vr*ice sheet from which they were taken originally. The tongues yin thefinished joint are conlined substantially to the same two levels orthicknesses of the metal sheets thus joined.

The struck-up outer-wall tongues and the base portions of the inner-walltongues acquire great strength when they are driven back into the holesleft in their original metal sheets. Each of the struck-up tongues actsas a tool whose location is fixed precisely in relation to the metal 0nwhich it is to act, operating accurately despite relatively inaccurateoperation of the pressure applying tools.

In forming a box with these joints in the illustrative disclosure, thetongue-driving tools employed are the same ones which bend the secondpair of walls up from the flat sheet-metal blank. The second pair ofwalls are bent into into the spaces in fthe underlying or inner sheetfrom y l,which the tongues were originally struck. Integral otiset areasextending from the outer sheets are thus formed in the joint-formingoperation. The portions of the inner-sheet tongues which formed theintegral oifsets then loccupy the spaces in the outer wall left by metalshifted in forming the offset.

Only part of each of the inner-wall tongues described overlies anintegral offset. The remainder of each inner- Wall tongue is forced backinto the space in the inner metal sheet from which it wasstruckinitially. This is achieved through the provision of a further lancestruck up from the outer sheet. This lancing operation forms relativelylarge holes for readily admitting the projecting tongues of the innersheet metal elements.

-The struck-up tongues of the outer sheet metal walls are driven againstthe base portions of the inner-wall tongues.

ut'ongues back into the initial spaces in the inner metal place bywiping dies, and those wiping dies continue their motion to wipe overthe projecting tongues and drive them into final configuration.

The tongues struck up from the inner and outer sheets are arranged so asto extend from their base connections in the same direction relative tothe holes left in their original sheets. In the box this is upward, awayfrom the bottom of the box and toward the edges of the box. It is byvirtue of this arrangement that the same wiping dies which fold thesecond pair of walls up into position are also effective in the verysame stroke for completing the joints. Consequently, certain steps inhandling of the box are avoided, such as might be required in making abox and then making joints of comparable strength. The cost of makingthe box complete with the novel joints is not appreciably different fromthat of making the box without joints.

The holes in the outer wall are made larger in all directions than thecross section of the inner-wall tongues which extend outwardly throughsuch holes during the forming operation. This is an importantconsideration since it enables practical joint-fabrication withoutimposing unduly close tolerances on various dies involved in the usualsequence of blanking, piercing and lancing, and bending stations. Theapplication of the novel joint to the box described is highlyadvantageous but is not intended to be limiting since the inventionobviously has useful application to a wide variety of structures otherthan this form of sheet metal box.

In the accompanying drawings in which an illustrative embodiment of theinvention is shown:

Fig. l is a perspective of a box embodying features of the invention,the proportions of the joints being greatly enlarged relative to thedimensions of the walls of the box;

Fig. 2 is an enlarged fragmentary front view of a joint before the partsare bent into interlocking engagement; Fig. 3 is a cross section of thejoint along the line 3-3 in`Fig. 2;

Figs. 4 and 5 are progressive cross sections of the parts of Fig. 3 inintermediate and final conditions, respectively, the plane of thesection being the same as lthat of Fig. 3;

Fig. 6 is a cross section, further enlarged along line 6-6 of Fig. 5;and

Fig. 7 is a reduced cross sectional view of a metal box blank andforming dies preparatory to the linal side-folding and joiningoperation, the plane of the section of this View being represented bythe line 7j-7 in Fig. l.

Fig. 1 illustrates the invention as applied to a four-,- Walled openbox. This View shows a pair of end walls 10 having `in-turned edgeportions or inner walls 12 and having outer side walls 14 all extendingupward from the bottom 18. Near each corner of the box a mechanicaljoint is shown, formed of two tongues 12a and 14a, these numberscorresponding to the sheet metal elements from whichthey extend. As seenin Fig. 5, tongue 12a includes an end portion 12b and a further baseportion 12e, the first portion being disposed over the outside surfaceof outer wall .14 yet being disposed in the level or thickness of thatmetal sheet, and the tongue portion 12e is disposed within the originallevel or thickness of inner metal sheet 112 from which it was initiallyformed. An integral off-set area 14b is formed of wall 14, this beingvery nearly of the same outline as tongue portion 12b. Offset 14b isformed (as will be seen) by pressurt applied by tongue pottion 12b.

The upper edge of tongue portion 12b is seen to be intimately dug intothe wall 14, immediately opposite the hole in panel 12 left by cuttingtongue 12a out of metal sheet 12; and similarly, the upper edge oftongue 14a and the lower edge of off-set 14b grip and dig into and lockthe portion of tongue 12a at the line between portions 12b and 12C. Thisresulting interlocking arrangement prevents even the slightest motion ofouter sheet 14 relative to inner sheet 12 if there were any tendency ofthe sheets to shift in the vertical direction.

As seen in Fig. 6, tongue portion 12b has pressed a small integral area14b of Wall 14 into the hole left in sheet 112 when tongue 12a was cutfrom the sheet. Offset area 14b, pressed into that hole by tongueportion 12b leaves a corresponding recess at the level of sheet 14, andthat recess is occupied by tongue portion 12b. Because of the interlockformed at the lateral edges of tongue portion 12b and off-set area 14b,no sliding motion of sheet 14 relative to sheet 12 is possiblehorizontally in the plane of those sheets.

Tongue 14a is driven into the space in its own sheet metal member fromwhich it was originally formed, and similarly tongue portion 12a`occupies substantially the original space in the inner sheet from whichit was taken. This is no easy t. When each such a tongue is cut out ofits original sheet metal member and then driven back, there is greatbinding at the edges, and considerable force would be required to drivethe tongue out of its original hole. These edge binding forces developconsiderable resistance to any force tending to pull sheet metal Vmem'-ber 14 from sheet metal member 12. Tongue 14a prevents tongue portion12c from being pulled out of the position shown and tongue portion 12Citself is edgelocked in its original sheet.

It will be understood that if one were to attempt to separate sheets 12and 14, it would be necessaryto bend small integral area 14b from itsposition where it is overlapped by tongue portion 12b, or tongue portion12b would have to be bent into upright position; and in order to dothis, all of the various edge binding forces would have to be overcome.

It has been noted that the proportions in Fig. 1 are distorted.Illustrative dimensions are: a box having a panel of 41/2" wide and 3deep, approximately, and an in-turned edge portion 12, 1/2" wide,utilizes a tapered lug 12a that is only 5/16" high by 3A6 wide at itsupper edge and '5/16" wide at its base or point of connection toin-turned metal sheet 12; and in panel 14 that is 6" wide by 3" high,tongue 14a is 5% high, with an upper edge of 1%2", slightly tapered tohave a broader base where it connects to its original sheet. `In sheetmetal of .054" thickness and only one such joint per corner, a box hasbeen tested for Underwriters Laboratories approval, and found to be sostrong as to involve severe warping of the walls without damage to thejoints. The strength of the box compares favorably with a box having anumber of spot-welds at each corner. The great strength of the new jointis maintained with remarkable uniformity, over a large number of boxesin mass production.

The box of Fig. 1 is formed in a series of blanking, piercing andbending operations which are, in general, entirely conventional and arenot illustrated. The sheet metal is formed and the tongues 12a and 14aare assembledas illustrated in Figs. 2 and 3. Off-set area 14b has notbeen formed, and is represented in Fig. 3 by vthe numeral 14b'. Tongue12a is seen to project perpendicularly from sheet 12 through hole 14cleft yin sheet 14 by the formation of tongue 14a. Hole 14C is` seen tohave its edge displaced by the distance 14b' from the upper edge of thehole 12d that was left in sheet `12 when tongue 12a was formed.

It is relatively simple and a relatively non-critical operation toassemble the sheets in the condition shown 1n Figs. 2 and 3, for thereis a very great latitude permitted by the difference in size of thecross-section of tongue 12a, as viewed end-wise in Fig. 2, and theaperture which tongue 12a is to penetrate. Thus, the side-to-sidetolerance is very great, the spaces A in Fig. 2 allowing a substantiallatitude of error in arranging for tongue 12a to project through sheet14. Similarly there is a considerable space between the upper edge 14Cand the upper edge of tongue 14a for the tongue 12a to enter and bereceived. The vertical clearances left between tongue 12a and the holeit is to enter are represented by spaces B and C in Fig. 3. This is afeature of immense importance in the practical application of this jointfor it permits a wide range of variation and a comparatively great errorin setting up of the tools without harmful effect in the assembling andjoining operations and in the resulting joint.

With the assembly shown in Figs. 2 and 3, the joint is made by applyinga force to the lower surface of tongue 14a. It should be noted that theouter end of tongue 14a has a curled portion 14d. This curled tongue endengages the lower face of tongue 12a perpendicularly and acts as alocalized tool which bends tongue 12a as tongue 14a is being bent. Thebending operation is complete as shown in Fig. 4 with tongue 14a pressedagainst the outside surface of tongue 12a and tongue 12a pressed againstedge 14e of metal sheet 14. As shown by a comparison of the views inFigs. 4 and 5 the joint is transformed preferably by sliding a tool upalong the outer face of metal sheet 14 while furnishing backing forsheet 12, or a slant blow may be struck against the outer faces oftongues 14a and 12a. In box manufacture, either procedure can befollowed in the same station where the sides of the box are bent up.During this final phase of the joint formation, tongue 14a drives tongueportion 12e into that portion of hole 12d from which that tongue portionwas originally taken, and tongue 14a is itself substantially returned tothe portion of the sheet 14 from which it was taken; and tongue portion12b forms an off-set area 14b extending integrally from the sheet metalwall 14. Tongue portion 12b is seen to have driven area 14b into thespace left in metal sheet 12 when tongue portion 12b was originallyformed, and, in turn, tongue portion 12b is seen to occupy the spaceleft in sheet 14 by the formation of area 14b. The only mechanicalworking of sheet 14 that is imposed in forming offset 14b occurs duringthe very operation of forming the joint. There is no mechanical workingof the metal at the edges of this offset preparatory to making thejoint. Avoidance of such double mechanical working of the metal inmaking this oifset is of substantial importance to the strength of thejoint. Similarly, the only mechanical working of tongue portion 12boccurs during the formation of the joint. Tongues 12a and 14a are formedwith a bend of generous radius at their connections to their respectivesheets, and are thus protected from excessive mechanical working.

It has been 'said that this particular form of joint has specialadvantage in application to a box, of the general form shown in Fig. l.The joint possesses all the requisite strength. The tongues are formedin the 'same stations where other holes, tongues and knock-outs areformed in the box blank; and the joint can be formed in the very sameoperation required to bend the sides of the box into upright conditionin the routine manufacture of such boxes. The folding operation isillustrated in Fig. 7. The box blank, whose portions bear the samereference numerals in Fig. 7 as the box shown in Fig. l, is supported ona male die 20 and is held against that vdie vthat they penetrate holes14C when the side walls 14 are bent into vertical position by thesliding female die 24. As the die wipes across the outside walls 14,that `die strikes all of the tongues 14a simultaneously so as totransform the assembly through the succession of conditions shown inFigs. 3, 4 and finally 5. In Fig. 7, tongues 12a extend across the pathof die 24, and in the finished joint, tongues 12a are directed away fromthe bottom of the box. The same direction of bending is effected whenthe joints are formed as is involved when the side walls are bent intovertical position.

Some of the minor but significant detailed features may be of interest.The upper edge of tongue 12b is offset somewhat below the upper edge ofhole 12d, because of the sinuous form of tongue 12a as it passes betweenoffset :14b and tongue 14a. Tongue 12b has tapered edges. It is byvirtue of the offset between the tongue parts 12a and :12b and the taperof the latter that the transverse dimension of tongue 12b vis everywhereslightly narrower than that ofv offset area 14b. Offset 14b accordinglyis joined to its sheet 14 not only at its base but alsoat its Theforegoing detailed of the invention. However, it will be recognized thatvarious features of the invention have a range of useful application,and the general arrangement, and the details of the illustrativeembodiment are subject to a latitude of variation. Consequently,` theappended claims should be accorded a latitude of interpretation,consistent with the4 spirit and scope of the invention.

What is claimed is: 1. The method of joining two metal sheets togetherincluding the steps of striking a first relatively narrow and longtongue up from the first sheet to leave a first hole therein and withsaid tongue projecting outward thereof, striking a second relativelyshort and broad tongue up from the second metal sheet to leave a secondhole therein, and forming a curled end on said second tongue, thereafterassembling the sheets in overlying relationship with the tongue of thefirst sheet extending through the hole in the second sheet and with thecurled end on said second tongue extending toward the first tongue,driving the curled portion of the second tongue against the firsttongue, and driving a projecting portion of the first tongue against thesecond sheet, and forcing both said tongues to occupy the thicknesses ofsaid sheets, respectively.

2. The method of making a metal box which includes the steps of forminga sheet-metal blank with opposed pairs of walls, forming upstandingrelatively narrow tongues in laterally extending portions of one pair ofwallsso as to leave holes in such laterally extending portions and withthe tongues extending integrally therefrom, forming second relativelywide tongues in the second pair of walls, leaving correspondingapertures in the second pair of walls, with the apertures in position toreceive the upstanding tongues when the blank is later bent into boxform, and to provide a wall portion overlying the holes in saidfirst-mentioned tongues, forming a curled end on each of saidsecond-mentioned tongues, with the curled ends of said second-mentionedtongues extending toward said first-mentioned tongues bending thefirst-mentioned pair of walls into upright position, and bending thesecond set of walls so as to have the first-mentioned tongues projectthrough the holes in the second pair of walls, driving the curled endsof said second set of tongues against the first set of tongues andthereafter driving both sets of tongues substantially into the thicknessof the overlying walls from which the lances were struck.

3. The method of joining two metal sheets together including the stepsof striking a first tongue up from a first sheet to leave a first holetherein and with said tongue projecting outward thereof, striking asecond tongue up from the second metal sheet to leave a second holetherein and forming `a curled end on said second tongue, as-

sembling the sheets in overlying relationship with both tonguesprojecting from .the same side of the assembled sheets and with thetongue of the first sheet extending through the hole in the second sheetand with said curled end on said second tongue extending toward saidfirst tongue, driving the curled end of lthe second tongue against therst tongue, driving a projecting portion of the first tongue against thesecond sheet, and forcing both 4tongues to occupy the thicknesses ofsaid sheets with part `of the first ltongue occupying the thickness ofthe second sheet adjacent said hole therein and part of the second sheetthat underlies said part of `said first tongue occupying part of saidhole in the first sheet from which said first -tongue was struck.

4. The method of making a sheet-metal box which `includes the steps offorming a blank of sheet metal with a rectangular bottom, an opposedfirst pair of walls, lateral port-ions extending from said first pair ofwalls, and an opposed second pair of walls, striking relatively narrowintegral tongues up from said lateral portions `extending from saidfirst walls so as to project outwardly when said walls and said lateralportions are bent into box form, striking second relatively wide tonguesup from lthe second pair of walls so as to project outwardly when saidsecond walls are bent into box form, the holes left by striking up saidwide tongues being located to adm-it said relatively narrow tongues whenthe blank is bent into box form and the holes left by striking up saidfirst tongues being located so as to be in part covered by respectiveareas of said second walls when the blank is bent into box form, bendingsaid first pair of walls into upright position relative to said bottomand bending said lateral portions at right angles thereto, saidrelatively narrow tongues thereby projecting outwardly, bending saidsecond walls into upright position relative to said bottom and therebycausing said relatively narrow outwardly projecting tongues to projectthrough the holes left by striking up said second tongues and causingsaid relatively wide tongues to project outwardly, and driving both thenarrow and wide tongues in the restoring direction relative to the holesfrom which they were struck, the driving opera-tion being sufficientlyintense to force said second tongues and opposed portions of said firsttongues respectively back into the holes and substantially into themetal thickness from which they were struck and to drive additionalportions of said first tongues against said hole-covering areas of saidsecond walls intensely enough to offset said hole-covering areas intothe hole portions covered thereby and at the same time driving said`additional portions of said relatively narrow tongues substantiallyinto 4the thickness of the second walls to occupy the space Ileft vacantby ofi-setting of said areas as aforesaid,

5. The method in accordance with claim 4 wherein the holes left bystriking up said tongues are more remote from said bottom than theconnection of said tongues to said sheet-metal blank, and wherein saiddriving step as aforesaid is effected at least in part by a wipingstroke along the outside surface of the box in the direction away fromsaid bottom.

6. The method of making a sheet-metal box which includes the steps offorming a blank of sheet-metal with a rectangular bottom, an opposedfirst pair of walls and an opposed second pair of walls, and withlateral portions extending integrally from said first pair of walls, aportion of each of said second pair of walls to be engaged by one ofsaid lateral portions of said first pair 7 ofk walls as a pairofcompanion face-to-face contacting portions in the completed box,striking integral upstanding tongues out of said lateral portions andout of said portions of said second walls and leaving holes therein, the.tongues all projecting generally in the same direction relative to onesurface of the sheet-metal and relative to the bottom of the completedbox, the tongue that extends from one of each pair of said companionportion being relatively narrow and the tongue that extends from theother one of each said pair of companion portions being relatively wide,both tongues and the corresponding holes of each of said pairs ofcompanion portions being located so that each narrow tongue will enterand project through the hole left by the related wide tongue when 'saidlateral portions and said pairs of walls are bent into box form, andeach hole lef-t in one of a pair of said contacting portions by strikingup a said relatively narrow tongue being located to be partly covered bya small area of the other of said pair of contacting portions, bendingsaid iirst walls so as to be erect on said bottom and bending saidlateral portions at right angles to said hrst walls, bending said secondwalls so that said cornpanion portions thereof make face-to-face contactwith said lateral portions of said rst walls, the relatively narrowtongues projecting through the holes left by striking up the relativelywide tongues and said wide tongues projecting in the same generaldirection as said relatively narrow tongues, and driving both therelatively narrow tongue and the relatively wide `tongue of each saidpair of portions substantially into the thicknesses of such pair lofportions with part of each relatively narrow tongue being driven againstthe corresponding small hole-cover- `ing area with suicient intensity to.ofi-set said small 'area into thepart of the hole covered thereby andinto the -thickness of the metal in which such hole is formed,

said part of each narrow tongue being driven into the vspace originallyoccupied by said offset small area, each of said relatively wide tonguesbeing intensely driven against opposed portions of said relativelynarrow tongues so as to drive both the wide tongues and Ithecorresponding portions of the relatively narrow tongues backsubstantially into nthe metal thickness `from which they were struck and.into edge-locking relation therewith.

7. A four-walled sheet-metal box including a rectanguposed second pairof walls, lateral portions extending integrally from said lirst wallsand at right angles thereto and each lateral portion underlying acorresponding portion of one of said second walls at each corner of thebox, said portions at each Vcorner having respective integral tonguesstruck therefrom, one of said tongues at each corner being relativelywide and being edge-locked in the hole from which it was struck and theother of said tongues at each corner being relatively narrow and havinga part thereof underlying said relatively wide tongue, said part beingdisposed in the corresponding part of the hole from which it was struckand being edge-locked therein, an additional part of each of saidrelatively narrow tongues overlying a corresponding integral small areaof the related one of said portions adjacent the end of thecorresponding relatively wide tongue, each said additional part of saidrelatively narrow tongues being disposed to occupy .the thickness ofsaid portion from which the related second tongue extends land each saidsmall area being disposed to occupy the thickness of said portion fromwhich said rst tongue extends, both said tongues at each corner of thebox extending integrally from their respective portions in substantiallythe same direction.

8. A sheet-metal box in accordance with claim 7, wherein said relativelywide tongues are integral portions of said second walls and saidrelatively narrow tongues are integral portions of said lateral portionsof said rst walls, and wherein said relatively Wide and narrow tonguesextending in the upward direction relative to the bottom of the box.

References Cited in the le of this patent UNITED STATES PATENTS 6,647Pratt Aug. 14, 1849 V454,636 Brown I une 23, l1891 518,767 Plecker Apr.24, 1894 597,056 Dieckmann June 11, 1898 1,557,066 Krantz Oct. 13, 19252,426,670 Cooley Sept. 2, 1947 FOREIGN PATENTS 338,139 France Mar. 11,1904

